Facebook API get user accesstoken for app

I am posting to my facebook wall through my app using my 开发者_如何学Cuser. I gave to the app offline access but still, sometimes the accesstoken changes.

I would like to know if its possible to use Facebook API to get the accesstoken?

Right now, I used the example.php from the facebook sdk to login and took the accesstoken from there.

again, I dont want the application accesstoken. I want to user accesstoken of using the app.

Thanks.

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There is App Login section in Authorization paragraph in https://developers.facebook.com/docs/reference/api/ . Read it. You have to call it if you get invalid access token error in order to refresh the token. However, sometimes the token is invalid due to lack of permissions and not because the token is expired